The present invention relates in general to concrete tensioning apparatus, and more particularly to methods and apparatus for environmentally sealing tendons anchored to an anchor plate.
Various techniques exist for placing concrete slabs, floors, beams, and the like, under a tension to thereby strengthen the structure. The placement of a tension assembly in concrete is well known in connection with concrete slabs, such as are used for highways, bridges, floors and foundations. A popular post-tensioning technique is to support or otherwise suspend extruded plastic tubes or sheathes with greased tendons therein at locations that define the center of the concrete slab, when poured. The dead end of each tendon is anchored in an anchor plate at the factory by the conventional use of a pair of wedges. The live or stressing end of the tendons are not anchored at this time. Then, the concrete is poured around the tendon assemblies. After the concrete has been allowed a sufficient time to cure, the tendons are stretched to thereby place the concrete slab in compression. Each tendon is stretched against the near end anchor plate, and then a set of wedges are wedged between the tendon and the anchor plate, thereby leaving the tendon in a tensioned state. The end of the tendon that extends beyond the concrete sidewall is then cut by a torch, a saw blade, shears or other means. In order to protect both ends of the tendon where wedged to the respective anchor plates, the tapered pocket formed in the concrete is grouted in an attempt to environmentally seal the same. While the grouting technique may be effective in certain situations, it is not suitable in other situations. For example, the grout and concrete material itself is not entirely impervious to moisture, thereby allowing some degree of moisture to deteriorate the wedging connection to the tendon. Should such connection deteriorate over time, it is possible that the grip of the wedge on the tendon lets go, thereby releasing the tension in the cable. The significant advantage gained from the tensioned structure is then lost. Should one or more of the tendons become released from its tensioned state, it would not be known as it is difficult to determine when a tendon loses its tension.
In other situations, multiple tensions are run through a metal or plastic duct that extends through the concrete to be held in compression. An anchor plate having multiple anchor devices is utilized at each end of the multiple tendon assembly to thereby provide a combined tension in the concrete structure.
Various plastic caps have been devised by those skilled in the art to provide an environmental seal over the open end of the anchor plate, thereby preventing moisture and other contaminants from coming into contact with the tendon and wedge connection. In all of these end caps, a seal is attempted to be achieved between the end cap and the anchor plate. The most common connection is a mechanical connection of the plastic cap to the anchor plate itself. Because there are many different anchor plate configurations and styles, it becomes necessary to design an end cap that is specialized to mate with the particular style of anchor plate.
A similar problem exists in the fastening and sealing of connecting tubes to the back side of the anchor plates. The connecting tubes provide an interface between the plastic cable sheath and the anchor plate. Traditionally, this has been accomplished by forming the mating end of the plastic connecting tube so that it is friction fit over the base portion of the anchor plate. This neither forms a moisture seal nor a secure engagement of the mated parts. Rather, the connecting tube can be inadvertently pulled away from the anchor plate, there by allowing wet cement to enter into the assembly.
It can be seen that a need exists for an end cap that provides a high quality seal to the tendon end and tendon wedge connection. Another need exists for a seal cap that does not rely on the particular configuration of the anchor plate to achieve a seal of the tendon connection. Another need exists for a cost effective seal cap that is easily installed and with little effort. Another need exists for a cost effective technique for fixing the connecting tubes to the anchor plates and to also form a moisture seal.
Disclosed is a seal structure that overcomes the shortcomings and disadvantages of the prior art devices. In accordance with the principles and concepts of the invention, a seal cap construction is disclosed for reliably clamping to the tendon itself, rather than to the anchor plate. Disclosed also is a connecting tube that is securely fixed to the anchor plate, but provides a moisture seal therebetween.
In accordance with one embodiment of the invention, the seal cap is constructed of a plastic cap having a cylindrical or other shaped housing to abut against, or otherwise engage with a surface of the anchor plate. The seal cap includes a circular recessed area therein for attachment of a push nut. The seal cap is also constructed to include an internal receptacle for receiving therein the end of the tendon, when the seal cap is forced thereon. The push nut firmly grips the end of the tendon as the seal cap is hammered or otherwise forcefully pushed onto the tendon and into engagement with the anchor plate. Once driven to a home position onto the tendon, the seal cap does not retract whatsoever, thereby maintaining its position locked to the tendon, and in engagement with the anchor plate.
Various corrosion inhibiting mechanisms and sealants can be utilized with the seal cap of the invention. For example, a gel cap, grease, silicone or other sealing material can be placed in the tendon receptacle. Hence, when the seal cap is forced onto the end of the tendon, at least a portion of the corrosion inhibiting material is displaced so as to engulf the tendon end, and the wedge connection to the tendon. Other sealing mechanisms, such as a styrofoam washer, a gasket, O-ring or other rubberized materials can additionally be utilized to seal the skirt or edge of the seal cap to the anchor plate.
Other embodiments may include push nuts that are specially designed and shaped to accommodate the shape of the particular tendon that is utilized. In addition, electrical connections can be made via wires to the push nut so that external electrical access can be made to the tendon for either controlling corrosion thereof or for monitoring the tendon integrity.
According to another embodiment of the seal structure, there is disclosed a connecting tube that is constructed to employ a push nut for engaging with the base of the anchor plate. Much like the seal cap, the connecting tube also includes a closed cell foam washer to provide a seal between the connecting tube and the base of the anchor plate. Once the connecting tube is hammered onto the anchor plate, it is secured thereto and cannot be inadvertently removed.